Macroparticles are generated during sputtering by the presence of dielectric inclusions in the metallic sputter target. Electrical charges build up on the dielectric particle and eventually electrical breakdown occurs. When this electrical breakdown occurs a high current density cathodic arc forms and melts a small section of the target. The arc pressure causes the liquid metal in the cathode to spurt out at high velocity and strike the intended substrate. The droplets solidify on the substrate creating a large defect in the metallization layer.
This problem has been frequently experienced in the sputtering of large flat panel displays that commonly operate at power densities of greater than 16 W/cm2. The appearance of macroparticles on these flat panel displays causes gaps or shorts in the metallization patterns required for addressing the various pixels in the display. Obviously, the gaps or shorts reduce the yield of acceptable display units.
Sputtered aluminum layers are often the initial conductive layer that is coated on the substrate. In addition to the desire in having low inclusion levels in the Al target, the targets must also provide good resistance to hillock formation. It is known that alloying additions of silicon and copper are effective at reducing hillock formation and that these alloying additions to aluminum do not significantly lower the electrical conductivity of the resulting sputtered Al films.